1. Field of the Invention
This invention relates to processes for pre-treating sorbent compositions employed in desulfurization systems. In another aspect, the invention concerns a process for presulfiding a desulfurization sorbent in situ prior to using the presulfided sorbent composition to desulfurize a hydrocarbon-containing fluid stream.
2. Description of the Related Art
The increased global demand for cleaner burning fuels has driven the worldwide effort to reduce the sulfur levels in many hydrocarbon-based fuels, such as gasoline and diesel. Lower-sulfur fuel blends contribute to improved air quality by minimizing the adverse impact on emissions-regulating automotive components, such as, for example, highly sulfur-sensitive catalytic converters. Automobiles operating with inefficient or poisoned catalytic converters emit exhaust containing high levels of non-combusted, heavier-than-methane hydrocarbons, nitrogen oxides (i.e., NOx), sulfur oxides (i.e., SOx), and carbon monoxide. Catalyzed by sunlight, these components react to form ground-level ozone, more commonly referred to as “smog.”
In recent years, the public discussion regarding the reduction of sulfur levels in fuel blends has not focused on whether or not such a reduction should occur, but, rather, has centered on the required level of reduction, as well as the time frame for the implementation of corresponding regulations. Within the last several years, several countries, including China, the United States, Japan, India, Brazil, and the European Union have begun issuing mandates requiring progressively lower sulfur levels (e.g., some less than 10 ppmw) in automotive fuels, including both gasoline and diesel.
These stricter regulations have lead oil refiners and other fuel producers/blenders to alter their current fuel production schemes to include processes for desulfurizing the hydrocarbon-containing streams used as blendstocks for producing different types of consumer fuels, including, for example, typical automotive gasolines and diesels, heavy equipment diesel fuels, racing gasolines, aviation gasolines, boat gasolines, and the like. Examples of hydrocarbon streams used as blendstocks to produce these fuels include, but are not limited to, thermally and/or catalytically processed gasolines such as, for example, thermally cracked gasoline, visbreaker gasoline, coker gasoline and catalytically cracked gasoline (hereinafter collectively referred to as “cracked gasoline”).
At the same time, simultaneous increases in demand for refined products, such as gasoline, diesel, and related commodity fuels coupled with intensifying supply-side pressures have lead to record fuel prices. To maximize profits, especially in light of the additional capital investment and operating expense associated with the newly-added desulfurization process step, have caused refiners to strive to increase the time gasoline-producing units are operational (i.e., unit up-time or on-stream time). In order to properly maintain these process units, however, operators must take the units “offline” (i.e., suspend production to repair and clean the unit) to ensure efficient and safe unit operation. It is desirable to minimize these downtimes and to return to maximum production mode as quickly as possible in order to maximize profits.